This paper obtained an additively manufactured high-strength Al-Li alloy by laser powder bed fusion (LPBF) based on a third generation AA2195 alloy powder raw material. The relationship between the process optimization, microstructure evolution, and mechanical properties of the as-printed (AP) and heat-treated (HT) specimens was established for the first time to explain the intergranular fracture sensibility during LPBF and reveal the dominant precipitation strengthening mechanism induced by the subsequent heat treatment. The precipitation order of AP Al-Li alloy at the last stage of the solidification process was: L (Liquid phase) →T2 (Al6CuLi3) + θ′(Al2Cu) + δ′/β′ (Al3(Li,Zr)) + T (LiAlSi) + Ω (AlCuMgAg). The micro-cracks caused by a relatively high grain boundary coverage of interconnected film-like eutectic phases, as well as micro-voids caused by the localized slip between the coarse T2-phases and soft precipitate-free zones, resulted in the high intergranular fracture sensibility. The well-designed T6 heat treatment of 515 °C/60 min solution treatment and 170 °C/6 h aging treatment was conducted to maximize the precipitation strengthening by T1-phases. The precipitation order of HT Al-Li alloy was supersaturated solid solution → GP zone + δ′/β′ → θ′ + T1 (Al2CuLi) + ω (Al7Cu2Fe) + β′. The presence of continuously distributed T1-cells along the grain boundaries was not only capable of providing a pinning effect on dislocations movement and boundary migration, but also able to shorten the pile-up distance on the slip plane. Such phenomena improved the resistance ability of Al-Li alloys to mechanical damage and permitted a significant strength enhancement.
In this paper we propose a gold-plated photonic crystal fiber (PCF) refractive index sensor based on surface plasmon resonance (SPR), in which gold is coated on the external surface of PCF for easy fabrication and practical detection. The finite element method (FEM) is used for the performance analysis, and the numerical results show that the thickness of the gold film, the refractive index of the analyte, the radius of the air hole in the first layer, the second layer, and the central air hole can affect the sensing properties of the sensor. By optimizing the sensor structure, the maximum wavelength sensitivity can reach 11000 nm/RIU and the maximum amplitude sensitivity can reach 641 RIU−1. Due to its high sensitivity, the proposed sensor can be used for practical biological and chemical sensing.
With the deepening professionalization of Chinese sports,the sports broker industry has been developing rapidly.However,inadequate legislation and deficiencies in the regulatory system of sports brokers are hindering its further development.To ensure the healthy and sustainable development of the sports broker industry in China,the only way is to improve the legislative systems for sports brokers,access to legal regulatory systems and sports broker contract system and credit system.
High strain rate multi-directional forging (HSMDF) is an effectively method to expand the industrial application of Mg alloys. However, dynamic recrystallization (DRX) and strengthening mechanisms of the HSMDFed Mg alloys are not understood. In this work, the evolution of LPSO phases and their roles on DRX of Mg-8Gd-1Er-1Zn-0.6Zr (wt.%) (GEZ811) alloy at various cumulative strains via HSMDF process are studied, and the corresponding strengthening mechanisms are analyzed. As the cumulative strain increases, the lamellar LPSO phase undergoes four stages: kinking, tearing, local breaking, and breaking into submicron particles, while the block LPSO phase is kinked, torn and broken with a long-plate morphology. DRX is the main reason for grain refinement of the HSMDFed alloy, in which the LPSO-induced DRX (LDRX) is dominant while the continuous dynamic recrystallization (CDRX) is complementary. The optimal comprehensive mechanical properties of the HSMDFed GEZ811 alloy are achieved at ∑Δ ε = 2.64, and its tensile yield strength, ultimate tensile strength and elongation are 302.4 MPa, 370.3 MPa and 11.8%, respectively. It is suggested that the combined strengthening effects of grain boundary, LPSO phase and dislocation are responsible for the enhancement of mechanical performance, among which the grain boundary strengthening is dominant. It is expected that the present work is beneficial to providing a low-cost approach for designing and fabricating the forged Mg-RE alloys with advanced mechanical performance.
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